The chief goal of this project is to understand the genetic mechanisms involved in antibody formation. Many investigations are focusing on the mechanisms of somatic diversification of antibody genes; this project will define the starting library, the inherited set, of immunoglobulin heavy chain variable region, Igh-V, genes of the BALB/c mouse. These studies will investigate the biological, genetic, and evolutionary factors which determine its composition and structure. The genetic analysis will be both Mendelian and molecular. The Mendelian analysis will proceed by analysis of genetic recombination in and around the Igh complex locus and by preservation of recombinant chromosomes as Igh Recombinant mouse strains. In these strains the expression of antibody markers (idiotypes and allotypes), neighboring lymphocyte alloantigen genes, and certain lymphocyte interactions will be characterized to define their regulation, roles and interactions in the immune response. The molecular analysis will proceed by recombinant DNA cloning of Vh genes and Southern blot analysis to determine the number of Vh genes and their relationships in homologous gene families. Analysis of the Vh libraries of disparate strains such as C57BL/6, DBA/2, A/He and NZB will characterize the nature and extent of polymorphism and delimit the biological requirements and allowed flexibility of these genes. The structure of the locus will be revealed by analysis of the recombined Vh arrays in the Igh Recombinant strains. Evolutionary changes and pathways will be identified by examination of the Vh libraries of a wide variety of mouse strains and substrains to characterize the processes of mutation, expansion, and contraction of Vh gene families. The utilization of each Vh gene and family to express antibodies of various specificities will be assessed by mRNA dot blot analysis of hybridomas and myelomas of known antigen binding specificity. The effects of polymorphic structural differences in V, D, and J sequences on idiotype expression will be investigated in Igh Recombinant strains.